1. Field of the Invention
The present invention relates to a novel process and apparatus for the production of foam products and, more particularly, a process and apparatus for preparing a polymer-based foam of a predetermined thickness that is produced without the need to slice a larger foam bun to the desired thickness. The resulting foam is suitable for use optimally as a surgical or medical dressing.
2. Background of the Invention
Historically, the treatment of wounds involved the application of sterile dressings such as gauze and lint to the injured area, both with and without the use of an antiseptic or curative substance. These dressing materials, however, suffer from a disadvantage in that they adhere to the surface being treated or leave fibers in the wound thereby prolonging the recovery period. In an attempt to circumvent the difficulties associated with the use of these materials, recent research and development efforts have yielded new products which are centered around the use of synthetic materials as wound dressings.
The processes by which these synthetic materials, such as films and sponges, are manufactured, vary according to the composition of the synthetic material and the properties desired in the final product. Nevertheless these processes possess many similarities. Generally, each process involves formulating a polymer-based foam precursor, providing a substrate, applying this foam precursor onto the substrate, and curing the resulting foam by applying heat. Such processes are typically extended by slicing a relatively thick foam bun into a final product having the desired thickness. However, the combination of the use of heat to effect curing as well as slicing the resulting product to the desired thickness increase the cost of the final product. Moreover, in the latter case, the addition of an extra step during production significantly lowers the overall efficiency of the process.
The determination of the amount of heat to effect curing of the foam material is further complicated by the desire to retain a certain amount of moisture in the final foam product. This moisture is preferred as it acts to enhance the appearance, texture, and wettability of the product. Thus, the use of heat to effect curing necessitates a complex analysis to determine the optimal amount of heat to use during the curing phase which will effect the proper curing of the foam while not resulting in the final product having less than the desired degree of moisture. Therefore, it would be advantageous to provide a process which would enable a manufacturer to easily produce a polymer-based foam product having a predetermined degree of moisture without necessitating the performance of a complex curing versus moisture loss analysis.
U.S. Pat. No. 4,660,553 illustrates a method for making a medical dressing. This process comprises applying a layer of a foamable silicone elastomer onto a substrate which is an absorbent for the composition. A scraper blade or the like is then used to distribute a critical amount of the elastomer onto the substrate. Reinforcing material is subsequently placed into the elastomeric composition and the reinforced foam is allowed to finally cure. In order to effect curing, the foam may be subjected either to ambient temperatures or to heat, the heat being applied to hasten or increase the degree of cure. After the foam has finally cured, the substrate is cut away from the foam product to produce a flexible, reinforced elastomeric foam sheet. The manner in which the elastomer is applied onto the substrate is the only means by which the thickness of the final foam product may be controlled in this process.
U.S. Pat. No. 3,959,049 discloses a process for making air permeable artificial leathers. This process comprises incorporating a catalyst, foam stabilizer, and optionally a pigment, into an isocyanate-terminated polyurethane prepolymer thereby forming a solvent free "paint". After the "paint" is formed, it is coated onto release paper and a substrate is applied over the exposed portion of the "paint". Subsequently, the foaming and polymerization reactions proceed in an atmosphere having a dry-bulb temperature between 40.degree. C. to 95.degree. C. and a relative humidity of at least 60 percent. The presence of heat and water at this stage of the process causes the reaction to advance. During the course of this reaction, the assemblage is passed through rollers which compress the assemblage. After the compression is completed, Examples 1-4 show the assemblage being placed in a dryer at 130.degree. C. for three minutes to further advance the foaming and polymerization reactions. The release paper is removed subsequent to this drying procedure.
Despite the variety of methods for the production of synthetic foams, there remains a need for a process for manufacturing a foam in which the thickness of the resulting foam may be accurately controlled. Further, this thickness should optimally be attainable without requiring a final slicing procedure. Moreover, it would also be advantageous if the process were more energy efficient, with no heating of the foam being required to effect the curing of the foam product.
Accordingly, it is a principal object of the present invention to provide a method for the continuous production of a polymer-based foam in which the thickness of the resulting product may be very accurately controlled.
A related object is to provide a method for the continuous production of a polymer-based foam in which the foam is formed directly to a predetermined thickness without the need to slice the foam to the desired thickness after curing.
Yet another object is to achieve a final product having a predetermined moisture level.
It is a further object of the present invention to provide a process for preparing a polymer-based foam product which is more efficient than prior processes wherein the application of heat to effect the curing of the product is not required.
An additional object is to provide an apparatus for accomplishing the aforesaid objects.
These and other objects and advantages of the present invention will be apparent from the following description of the invention.